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周固考研辅导讲义

　　Drastic times call for drastic measures, so state water agencies are turning to desalination, a technology that makes ocean and brackish water drinkable by stripping it of salt and other minerals. California has plans in various stages to build 13 desalination plants along its coastline. The projects will cost billions, but planners say theyll provide a far more reliable supply for California residents than waiting for Mother Nature to adjust her weather patterns.

　　Since just 3% of water on earth is fresh, this is a step that would have to be taken anyway as the global population grows. Desalination will create a drought-proof supply of water, says Bob Yamada, the San Diego Water Authoritys seawater-desalination program manager. He adds that 20 years from now, 10% to 20% of the states water could come from the ocean. The American Water Works Assn., a Denver-based nonprofit dedicated to improving drinking-water quality and supply, predicts that the market for desalination plants and equipment, now just $2 billion, will grow to more than $70 billion over the next two decades.

　　Environmentalists embrace desalination. Studies show that pumping the cooling water and concentrate back into the ocean raises its salinity by less than 1%, which is equivalent to the natural rise and fall. Barry Nelson, a senior policy analyst with the Natural Resources Defense Council, says he became a proponent of desalination when a June, 1999, California report demonstrated that it was cheaper than building new dams, which often have a huge environmental impact.